The present invention relates to a process for increasing the lifespan of metallic dental components such as root pins, implants, prostheses or bridges by means of a surface treatment of these components. In a further aspect, the present invention also relates to products produced by the foregoing process.
Metallic components generally cannot endure frequent random vibratory loads without undergoing fracture, even when the stress amplitude is relatively small in relation to the tensile strength of the corresponding materials as ascertained in a tensile test. Metallic components also often undergo fracture when the stress amplitude is smaller than the strain limit of the material employed. The behavior of the material is accordingly determined by the stress amplitude and the frequency of its repetition. In addition, the environmental conditions and the geometry of the components also have an effect on the fatigue strength under vibratory stress.
In the field of dentistry many components are intentionally (e.g., spring pins) or unintentionally (e.g., root pins) subjected to vibratory stress. Time and time again this results in the problem that components--although manufactured from an optimized alloy and adequately dimensioned, such as root pins or structural elements for example--fracture without material defects or processing faults subsequently being detectable. Investigations show rather that the components have failed by reason of material fatigue, which is further promoted by the environmental conditions in the mouth; e.g. exposure to saliva. One way of avoiding these fatigue fractures would be a greater dimensioning of the components in order to reduce the local stresses in the component. However, for reasons relating to the space situation in the mouth or for aesthetic reasons, this is often not possible. Such fractures can mostly be repaired only with great difficulty and considerable effort.
In vehicle and aircraft construction, shot-peening for improving the physical properties of metal objects has been known for many years and is employed successfully in these fields. The details of such techniques are described in many text books. For instance, it has generally been found that in respect of many components that have been subjected to shot-peening it has been possible to detect an increased fatigue strength. The increased fatigue strength in these cases is to be ascribed to the compressive stresses introduced into the surface layer which hinder the formation of cracks in the component. Thus in the field of vehicle construction, differential gears for vehicle axles, spindles, shafts, thrust collars and also connecting rods are shot-peened in order to increase their endurance strength. Also in the field of turbine construction, vanes that are utilized in the compressor part of the turbine are often shot-peened in order to increase the fatigue strength and hence the lifespan of the component.
Such techniques have not hitherto been adopted in the dental field. Neither have special processes for improving fatigue strength hitherto been taken into consideration.
Sand-blasting is employed in the dental field for the cleaning of castings, for example. However, as a result of the sand-blasting the quantity of material eroded is greater than the amount of deformation introduced into the surface layer. The surface of the components is therefore only roughed up. Since they are not overlaid by compressive stresses, these microscopic defects lead instead to a decrease in the fatigue strength of these components.
It was therefore an object of the present invention to develop a process for increasing the lifespan of metallic dental components such as root pins, implants, prostheses or bridges by means of a surface treatment without encountering the disadvantages of prior known strengthening techniques used in dental technology.